1. Field of the Invention
This invention relates to an apparatus of the type having a tool that is mounted at the distal region of an elongate pole and, more particularly, to such an apparatus wherein the tool is operated by a rotary force initiated by a drive at the proximal region of the elongate pole.
2. Background Art
Myriad apparatus are currently available having a tool mounted at the distal region of an elongate pole. One exemplary tool construction incorporates a chain that is driven guidingly in an endless path to cut small trees or branches. A user repositions the tool by manipulating the elongate pole from the proximal region thereof. At the proximal region of the elongate pole, a drive is provided for the tool. The drive typically is powered by a combustible fuel, household current, or a battery. The drive produces an operating drive torque at the output end of a power transmission assembly.
Power transmission assemblies in this environment currently exist in many different forms. In one of the simplest forms, a relatively inflexible shaft of fixed length extends between the tool and drive and has end couplings that are keyed to: a) be rotated by the drive; and b) rotate an input component on the tool to effect operation thereof. One example of this construction is shown in U.S. Pat. No. 6,880,248 (Weissert et al.).
The use of flexible shafts, of fixed length extending substantially fully between a tool and drive, is also known. This construction accommodates, among other designs, non-straight pole constructions.
Elongate poles with variable lengths are also known, as seen for example in U.S. Pat. No. 4,991,298 (Matre).
Regardless of the specific construction selected, designers of this type of equipment must contend with two, often competing, objectives: a) positive drive force transmission; and b) absorption of torque loading, and particularly shock loads. This is particularly a problem with respect to tools that incorporate chains for tree cutting. In this environment, the chain is prone to encountering significant cutting resistance and, in an extreme case, binding that significantly inhibits, or arrests, chain movement.
If no shock absorbing structure is incorporated, various system components are prone to being broken. This breakage could occur at the tool, shaft, and/or the drive. Such breakage may have serious direct and indirect financial consequences, particularly for those using equipment in businesses, such as landscaping.
It is known to incorporate clutch mechanisms into such systems, as at one or both ends of the power transmission assembly. While addressing the problem of shock loading, the clutch mechanisms potentially introduce other problems.
First of all, such mechanisms add another level of complication and cost to the overall design. More complicated structures generally also increase the likelihood of malfunction.
Secondly, the clutch mechanisms, to be effective, may lower the maximum drive torque below an optimal level.
A power transmission assembly that utilizes a flexible shaft, fully between a tool and drive, while potentially absorbing detrimental shock loads, may also introduce other problems. Most notably, it may not be possible to generate the desired level of drive torque.
Further, provision must be made to accommodate twisting and bending of a highly flexible component. This may complicate the system design and/or change its geometry in a detrimental matter.
It is also known, as the assignee herein does with certain of its equipment, to incorporate a short, flexible component at the input end of the power transmission assembly. This flexible component has been in the form of a coiled member having an overall length on the order of 3 to 6 inches, and a flexing length of approximately 4 inches. The ends of the member are keyed to the drive and a downstream component on the power transmission assembly. The intent of this design is to exploit the advantages of both rigid and flexible power transmission components, with the former desired for its positive force transmission capabilities, and the latter for its shock load absorption capabilities.
This design has reduced, to a certain extent, the failures associated with shock loading. However, there have nonetheless been an appreciable amount of failures in the field that warrant new designs for power transmission assemblies of this type.